Whether it's love for a romantic interest (likely that it is romantic between him and cas, but time will tell) or a family connection the darkness has no power over Dean when someone he loves is in danger.
If Cas learned this kind of love from Jimmy [powerful family love] it makes sense. And I personally think Dean taught him a different love, unintentional on Dean's part. I mean Cas cared deeply about his angelic family too.
Here, we see the moose confused. Suddenly the moose is distracted by a ray of light. And here is the moose being interrupted by an angry tiger. A very angry tiger. The crow seems pleased 《But Dean's a squirrel!